1. Field of the Invention
The present invention relates to a method for producing a structure.
2. Description of the Related Art
Diffraction gratings formed of structures having periodic structures have been used as spectroscopic elements for various apparatuses. In particular, structures composed of metals having high X-ray absorptivity have been used for nondestructive inspection of objects and in the medical field.
An example of the applications of structures composed of metals having high X-ray absorptivity is a shield grating in an image pick-up apparatus configured to pick-up an image using the Talbot interference of X-rays. An image pick-up method using the Talbot interference of X-rays (X-ray Talbot interferometry) is one of the imaging methods (X-ray phase imaging methods) using phase contrast of X-rays.
X-ray Talbot interferometry is briefly described. In a common image pick-up apparatus using X-ray Talbot interferometry, spatially coherent X-rays pass through a diffraction grating and a specimen which diffract X-rays to form an interference pattern. A shield grating configured to periodically shield X-rays is arranged at a position where the interference pattern is formed, thereby forming moire. The moire is detected with a detector. An image is obtained from the detection results.
A common shield grating used in Talbot interferometry has a structure in which X-ray shielding portions (hereinafter, also simply referred to as “shielding portions”) and X-ray transmitting portions (hereinafter, also simply referred to as “transmitting portions”) are arranged at a pitch of about 2 to about 8 μm, depending on imaging resolution required. The X-ray shielding portions are often formed of a structure which is composed of, a metal having high X-ray absorptivity, such as gold, and which has a high aspect ratio (the aspect ratio indicates the ratio of the height or depth h to the width w of a structure, i.e., h/w).
The shield grating having such a structure may be used to not only partially shield X-rays that form an interference pattern to form moire but also improve the spatial coherence of X-rays as described above. The shield grating used in this way is referred to as a “source grating”. When the source grating is arranged between an X-ray source and a diffraction grating, it is possible to virtually produce a state in which microfocus X-ray sources are arranged. A smaller focal point of an X-ray source (X-ray generating point) results in higher spatial coherence of X-rays generated from the X-ray source. Thus, the use of the source grating improves the spatial coherence of X-rays. Talbot interferometry performed by virtually forming the state in which the microfocus X-ray sources are arranged is referred to as “Talbot-Lau interferometry. The shield grating in this specification includes the source grating, unless otherwise specified.
As a method for producing such a shield grating, a method in which a metal is charged into a mold by plating is known.
Japanese Patent Laid-Open No. 2012-93332 discloses a method for forming a metal member by etching an etching substrate of a substrate in which an electrically conductive substrate and the etching substrate are bonded together to form a plurality of grooves and charging gold into each of the grooves by plating using the electrically conductive substrate as a seed layer.
In Japanese Patent Laid-Open No. 2012-93332, however, the electrically conductive substrate is likely to be etched, depending on an etching method of the etching substrate and the material of the electrically conductive substrate. If the electrically conductive substrate is etched, the starting position of charging of gold may vary.